Ammonia volatilization, greenhouse gas emissions and microbiological mechanisms following the application of nitrogen fertilizers in a saline-alkali paddy ecosystem

The application of nitrogen (N) fertilizer can promote rice yield, but is accompanied by considerable quantities of ammonia (NH3) volatilization and greenhouse gas (GHG) emissions. The effect of N-fertilization to these gas emissions in saline-alkali paddy ecosystems is unclear. A 137-day mesocosm-scale experiment was carried out to clarify the effect of different N-fertilizer application strategies on NH3 volatilization and GHG emissions in saline-alkali paddy ecosystems and to determine the microbiological mechanisms. Five N-fertilizer treatments consisting of control without N-fertilizer (CK), urea (U), urea with urease-nitrification inhibitors (UI), organic–inorganic compound fertilizer (OCF) and carbon-based slow-release fertilizer (CSF) were established. During the entire rice-growing season, the cumulative NH3 emissions of UI, OCF and CSF treatments were 22.60–25.55 % significantly (p < 0.05) higher than U, respectively. The cumulative methane emissions in all N-fertilizer treatments were decreased by 9.23–28.24 % compared with CK. The cumulative carbon dioxide emissions were U > CSF > OCF > CK > UI, and the cumulative nitrous oxide (N2O) emissions were U > CSF > UI > CK > OCF. The global warming potential of UI was 5.39–32.35 % lower than all the other treatments. Compared with the other N-fertilizer treatments, the relative abundance of N-related functional bacteria (e.g., Sphingomonas and Alphaproteobacteria) in OCF treatment was increased, and the (nirS + nirK)/nosZ ratio was reduced, thereby decreasing the N2O emission. Overall, U is a better choice for controlling NH3 volatilization in saline-alkali paddy ecosystems, whereas UI and OCF are more beneficial for reducing GHG emissions.